In a boiling water type nuclear power plant, various measures are taken to prevent an excessive increase in fuel canning pipe temperature at the time of a loss-of-coolant accident due to breakage of piping or the like connecting to a reactor pressure vessel. For example, at the time of emergency, a cooling material is injected into the core by an emergency core cooling system (hereinafter referred to as the “ECCS”), whereby the core is submerged. Through this operation of the ECCS, fuel failure is prevented, and core decay heat is removed. In conformity with the concept of safety equipment design, the ECCS is designed so as to be capable of securing the requisite safety even if there is single failure of the active component of each section or external power loss.
In the case of a total power loss accident, the system is designed such that, within a specific period, the core cooling is maintained by a reactor core isolation cooling system using a portion of the nuclear reactor vapor for turbine drive.
On the other hand, in the boiling water type nuclear plant, a countermeasure (hereinafter referred to as the “accident management”) is prepared for the purpose of further enhancing safety even when there occurs, through at a very low probability of occurrence, a severe accident substantially exceeding in scale the accident level to be imagined at the stage of design. For example, as accident management equipment utilizing existing systems, there is provided an alternate water injection system configured to supply cooling water to the reactor pressure vessel or the reactor containment vessel from a condensate storage tank by using a general service water supply pump, or from a fire-fighting water tank by using a fire pump.
PTL 1 discloses a technique according to which a back-up building surrounded by a hazard wall is provided at a place at a fixed distance from the nuclear reactor building, and this back-up building is equipped with an independent power source and an operating panel, thereby securing further safety.